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NAME | DESCRIPTION | JSON DATA SOURCES | SECURITY MODEL | INSTALLATION | FILES | PCP ENVIRONMENT | SEE ALSO | COLOPHON |
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PMDAJSON(1) General Commands Manual PMDAJSON(1)
pmdajson - JSON PMDA
pmdajson is a Performance Metrics Domain Agent (PMDA) which
exports metrics from arbitrary sources generating JavaScript
Object Notation (JSON) syntax.
At least one pair of JSON inputs are required for pmdajson to
provide metrics for PCP clients; one describing metric metadata
and one containing metric values data. Metadata is read once from
a file at PMDA startup while the data is read every time a request
for metric values is made by a PCP client. The data is read
either from a JSON file or an external command generating JSON
output. More than one pair of JSON inputs can be used to support
arbitrary number of metric sources in different configured
directories.
The overall JSON format description is at http://www.json.org/ .
pmdajson reads a mandatory JSON configuration file
• $PCP_PMDAS_DIR/json/config.json
This file can contain the following PMDA options using the JSON
syntax:
• directory_list
• trusted_directory_list
pmdajson searches the directories listed for these options looking
for files named metadata.json and (by default) data.json. The
JSON metadata files describe the metric names, types, and other
details of the associated JSON metric data. The JSON data file
name is configurable, and can also be an external command instead
of a periodically updated (by external tools) data file.
Each of these found JSON file/command pairs form a JSON data
source.
For example, let us assume the following simple JSON data file
that contains values for two metrics, one of type string and one
numeric:
{
"string_value": "testing, 1, 2, 3",
"read_count": 0
}
For these metrics the metadata file needed by pmdajson would be:
{
"metrics": [
{
"name": "string_value",
"pointer": "/string_value",
"type": "string"
},
{
"name": "read_count",
"pointer": "/read_count",
"type": "integer",
"description": "Times values read"
}
]
}
For further details on the JSON metadata format and options, see
the README file included as part of pmdajson installation.
JSON data sources listed for the directory_list option are not
trusted, meaning that if external commands to generate the needed
JSON data are used, these commands are run as user nobody.
JSON data sources listed for the trusted_directory_list option are
trusted, meaning that if external commands to generate the needed
JSON data are used, these commands are run as user root.
For further details on security and description on running
external commands, see the README file included as part of
pmdajson installation.
Install the JSON PMDA by using the Install script as root:
# cd $PCP_PMDAS_DIR/json
# ./Install
To uninstall, do the following as root:
# cd $PCP_PMDAS_DIR/json
# ./Remove
pmdajson is launched by pmcd(1) and should never be executed
directly. The Install and Remove scripts notify pmcd(1) when the
agent is installed or removed.
$PCP_PMDAS_DIR/json/README
additional documentation for pmdajson used JSON files
$PCP_PMDAS_DIR/json/config.json
configuration file for the pmdajson agent
$PCP_PMDAS_DIR/json/Install
installation script for the pmdajson agent
$PCP_PMDAS_DIR/json/Remove
undo installation script for the pmdajson agent
$PCP_LOG_DIR/pmcd/json.log
default log file for messages from the pmdajson agent
Environment variables with the prefix PCP_ are used to
parameterize the file and directory names used by PCP. On each
installation, the file /etc/pcp.conf contains the local values for
these variables. The $PCP_CONF variable may be used to specify an
alternative configuration file, as described in pcp.conf(5).
PCPIntro(1), pmcd(1) and pminfo(1).
This page is part of the PCP (Performance Co-Pilot) project.
Information about the project can be found at
⟨http://www.pcp.io/⟩. If you have a bug report for this manual
page, send it to [email protected]. This page was obtained from the
project's upstream Git repository
⟨https://github.com/performancecopilot/pcp.git⟩ on 2025-08-11.
(At that time, the date of the most recent commit that was found
in the repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
Performance Co-Pilot PCP PMDAJSON(1)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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